Process for the catalytic desulfurization of hydrocarbon oils



used to alimited extent in practice.

Patented Apr. 1, 1952 PRQCESS FOR THE CATALYTIC DESUL- FURIZATION OFHYDROCARBON OILS Willem Frederik Engel, Amsterdam, and Peter van tSpijker, The Hague, Netherlands, assign? ors to Shell DevelopmentCompany, San Francisco, Calif., a corporation of Delaware No Drawing.Application December 21, 1948, Se-

rial No. 66,578. In the Netherlands December 6 Claims. 1

This invention relates to an improved method for the treatment ofsulfur-bearing hydrocarbon oils under conditions of elevated temperatureand high pressure to remove sulfur without substantial decomposition ofthe oil treated. More particularly the invention relates to an improvedmethod for the removal of organically combined sulfur from heavy oilssuch as gas oils, lubricating oils and the like materials boiling abovethe gasoline boiling range.

The partial removal of sulfur from hydrocarbon oils takes place, atleast to a certain degree, in numerous oil-treating processes. Thus, forexample, such oil-treating processes as thermal cracking, catalyticcracking, thermal reforming, catalytic reforming, hydrcforming,alkylation, polymerization and isomerization usually result in someremoval of sulfur from the oil treated.

In fact, an appreciable amount of sulfur is often problem. While manysolutions have been proposed and some of them have been tried, it isnevertheless a fact that at the present state of knowledge thedesulfurization of hydrocarbons in anything approaching an eflicientmanner is a very costly operation which is rarely justifiecfin theeconomy presently pervailing.

While certain other types of processes may have some limitedapplication, the desulfurization process generally considered the bestat prescut is one in which the oil is treated in the vapor phase in thepresence of a large excess of hydrogen and a sulfactive hydrogenationcatalyst under moderate conditions of temperature and pressure. Thisprocess is described in numerous patents and articles in the tradejournals and has been This proeess, of which ther are numerous minorvariations, is fairly efiicient, but the cost of the plant and the costof operation are so high that the process is rarely economical. Thisvapor phase desulfurization process is theoretically applicable to thedesulfurization of any hydrocarbon oil, but from a practical standpointit is limited to the desulfurization of light hydrocarbon oils such asgasoline, kerosene, light gas oils and the like, oils .which are easilyvaporizable without decomposition.

The desulfurization of heavy hydrocarbon oils (Cl. 19t 28) hydrogenationconditions.

presents a still more diflicult problem. Such oils can be and have beendesulfurized fairly efiiciently by treating them under otherwise similarconditions while they are completely or partly in the liquid phase. Theplant costs and the operating costs are also prohibitively high in thiscase. Also, the reaction rate is slower than in the vapor phase processand the periodic regeneration of the catalyst is mademuch more difficultby the presence of liquid oil in the reactor.

The largest single factors causing the high capital costs and operatingcosts in the mentioned processes are the cost of the considerableamounts of hydrogen required and the cost of the facilities for handling(storage, separation, compression, recycling, preheating, etc.) thelarge amounts of high pressure hydrogen. In an attempt to overcome thisdisadvantage it was tried to supply the required hydrogen by thesimultaneous, dehydrogenation of added naphthenic hydrocarbons. Whilethe presence of added naphthenes afforded a small improvement indesulfurization over that obtained without their presence, not more thanhalf, and usually only about one quarter of the sulfur could be removedby this method, even when treating a light oil in the vapor phase. Also,under these conditions the life of the catalyst was too short to bringthe process into practical consideration. When operating the processwith large amounts of recycled hydrogen to improve the lif of thecatalyst the presence of added naphthenes decreased the consumption ofhydrogen somewhat when operating at the heighest permissibletemperatures. However, there was still a prohibitive consumption ofhydrogen and the main items of cost were not materially reduced. Theonly metho found for eliminating the net hydrogen consumption was totreat the napthenic hydrocarbon separately under dehydrogenationconditions and then use the product gas for the treatment of the oil tobe desulfurized under This increases, rather than decreases, the plantcosts and operating costs and is in effect only the substitution of aseparate dehydrogenation process for one of the other usual methods forthe production of hydrogen. It is, therefore, only a solution in the fewisolated cases where the dehydrogenation of large amounts of naphthenesis a profitable operation of itself. This was frequently the situationduring the warwhen large amounts of toluene were produced by thedehydrogenation of methyl cyclohexane fractions from petroleum, but itis rarely the situation now.

It has now been found that hydrocarbon oils boiling above the gasolineboiling range may be desulfurize in a practical and eflicient mannerwithout the use of extraneous hydrogen if the desulfurization is carriedout in the specific manner now to be described. In the method used by usthe oil to be desulfurized is first mixed with a lower boilinghydrocarbon oil (preferably having a lower sulfur content and being nottoo paraffinic in nature) to lower the critical temperature to wellbelow the operating temperature, and the mixture is then treated in theabsence of added hydrogen under specific conditions of temperature andpressure where transfer of hydrogen is favored and at the same time thedeposition of polymers, asphaltic materials, and similar materials onthe catalyst is largely prevente by the solvent action of the mixture.

The process of the invention is applicable for the desulfurization ofvarious hydrocarbon oils containing organically combined sulfur asimpurity, such, for example, as diesel fuels, socalled jet fuels, stoveoils, gas oils, spray oils, spindle oils, transformer oils, lubricatingoil distillates and the like materials boiling above the gasolineboiling range. The oils to be treated may have been obtained frompetroleum, coal, oil shale, or the like carbonaceous materials by widelydivergent physical or chemical treatments such as distillation,extraction, retorting, destructive hydrogenation, and thev like. Theprocess is particularly adapted for the treatment of heavy hydrocarbonoils, i. e., hydrocarbon oils having mid-boiling-points (A. S. T. M.) ofat least 200 C. and preferably above 250 C. The process is best adaptedfor the treatment of hydrocarbon oils having sulfur contents of at least0.1% and preferably at least 0.5%.

The process of the invention can be carried out with any of thesulfactive hydrogenation catalysts such as conventionally usedheretofore for hydrodesulfurization, destructive hydrogenation,hydrofining and related processes. The preferred catalysts have as theirmain active ingredient one or more hydrogenating oxides or sulfides ofthe transition metals (see J. Chem. Ed. 21, 532 (1944)) particularlythose of groups I, II, VI, and VIII of the periodic system of theelements. These materials may be used in various combinations with orwithout such stabilizers and promoters as the oxides or carbonates of K,Ag, Be. Mg, Ca, Sr, Ba, Ce, Bi, Cr, Th, Si, Al and Zr. These variouscatalysts may be applied per se or in combination with variousconventional supporting or carrying materials which in certain cases mayimpart very important characteristics to the catalyst. Examples of a fewtypical and preferred materials are activated aluminas, activatedmagnesias, activated silicas, activated zirconias, activated clays,activated bauxites and activated bleaching earths. (The term activatedis here used as denoting a material having a microporous structureaffordinga large inner surface.)

While any of the mentioned classes of conventional catalysts may beused, it is found that in this particular process some catalysts of thegeneral type are much better suited than others. .It was found that amolybdenum oxide catalyst promoted by a minor amount of cobalt oxide andsupported upon an activated alumina is quite superior to the severalother catalysts of the same general type. This preferred catalyst issomewhat similar to that described in U. S. Patent No. 2,393,288, butdiffers therefrom in that the oxides of molybdenum and cobalt areincorporated by impregnation in a previously activated alumina and themole ratio of molybdenum to cobalt is about 5 to 1.. The pro-activatedalumina is also preferably pretreated with a dilute solution ofhydrochloric acid or more preferably a 10% solution of hydrofluoric acidprior to the impregnation. This is the subject matter of copendingapplication Serial No. 82,285, filed March 18, 1949. The catalyst may befurther improved for the present purpose by the inclusion of a smallamount (for example, 2 to 6%) of silica and/or a small amount (forexample, 1 to 4%) of zinc oxide, as described in U. S. Patent 2,508,014of D. D. Davidson. The zinc oxide, it is found, should be impregnatedinto the activated alumina prior to the impregnation with the molybdenumcompound and cobalt compound. While these particular, more or lessspecial catalysts are superior in the present process to all of theother catalysts tried, the process of the invention is not restricted tothe use of these catalysts since in some cases it will be moreeconomical and practicable to use a somewhat less efficient but cheapercatalyst which can be discarded or easily regenerated after a shortperiod of use. The particular choice of catalyst will in practice dependto a large extent upon the particular material to be treated and itsintended use. In desulfurizing costly materials for final use (forexample, transformer oils and lubricating oils) where it is particularlyimportant to avoid side reactions such as cracking, isomerization,aromatization and the like, the catalytic agent is preferably combinedwith a special carrier material having relatively large micropores, suchas the new so-called beta alumina carriers or ordinary activated aluminawhich has been subjected to a relatively drastic pretreatment with steam(for example, at a temperature in the order of 4.00 to 600 0.). In othercases, for example in the partial desulfurization of reduced crudepetroleums, shale oils or the like materials preparatory to convertingthem into more useful products by catalytic cracking or relatedprocesses, a cheap catalyst such as an activated bauxite impregnatedwith small amounts of molybdenum oxide and cobalt oxide may beadvantageously used.

The sulfur removed from the hydrocarbon oil in the present process isremoved in the form of hydrogen sulfide. This hydrogen sulfide is notformed by hydrogenation of the sulfur compounds with free hydrogen addedor produced in situ, but by hydrogen transfer within the oil itself. Acarefully controlled temperature is necessary. Hydrogenation anddehydrogenation are opposite directions of one and the same fundamentalreaction. The direction of the .reaction, (1. e., Whether hydrogenationor dehydrogenation takes place) depends upon the temperature inaccordance with the known laws of thermodynamics. At low temperatures inthe order of 300 C. hydrogenation is favored; at high temperatures inthe order of 475 C. and above dehydrogenation is favored. In the smallintermediate range from about 325 C. to about 450 C. the system is nearequilibrium and any hydrogenation or dehydrogenation is of small extent.It is within this narrow range and most preferably between 375 C. and.425 C. that the desulfurization according to the present process iscarried out. In this range of temperatures the hydrogen bonds arerelatively labile in the presence of the catalyst allowing hydrogentranstier reactions to take place with a minimum amount ofdehydrogenation. As will be explained later, it is not only importantthat temperatures in this range be applied in order to take advantage ofthe optimum activity of the catalyst and the optimum conditions forhydrogen transfer, but also for other reasons.

The desulfurization is carried out in the presout process under highpressures in the absence of a liquid phase. In order that a liquid phasemay be positively excluded it is necessary to operate at a temperaturewhich is above the critical temperature of the material treated, andpreferably above the cricondentherm (the secand critical point). Thecritical temperature of any ,given oil to be treated can be calculatedwith sufiicient accuracy for the present purpose as described inIndustrial Engineering Chemis try, vol. 20, pages 1169-1172 (1928). Asomewhat more refined method is described in Industrial EngineeringChemistry, vol. 24, page 819 (1932). The oils to be desulfurizedgenerally have critical temperatures above 405 C. and often above 450 C.The cricondentherm is generally only a few degrees (e. g., 20 C.) abovethe critical temperature. It is, therefore, preferred to operate at atemperature at least 20 C. above the critical temperature of thematerial treated.

The above-specified operating temperatures of 325-450 C. are eitherbelow the critical temperature of the oil to be desulfurized orsufficiently close thereto that separation of a liquid phase is notprecluded. According to the present method .a sufficient quantity of alower boiling hydrocarbon oil is added to the oil to be desolfurized tobring the critical temperature of the mixture down to below theoperating temperature and preferably at least 20 C. below the op eratingtemperature. The amount to be added in any given case is easilycalculated as indicated above.

The oil added, as indicated above, is a lower boiling hydrocarbon oil.However, for reasons which will be apparent the'added oil should not betoo volatile. The preferred material is a naphtha boiling substantiallywithin the range of about 100 C. to about 205 C. As will be furtherexplained, the added oil is not materially altered in the treatment; itis frequently desired to recycle it in the process after separating itfrom the desulfurized oil. When it is desired to do this the boilingrange of the added oil should also be chosen to allow easy separationfrom the desulfurized oil by distillation.

The character of the added oil is also important. It is found that ifthe added oil is too paramnic in nature it tends 'to cause precipitationof tarry materials from the reaction mixture. It is, therefore,desirable to choose an oil containing less than 50% parafiins.Naphthenic naphthas are quite suited. The added oil may contain somesulfur impurities, but it preferably contains less sulfur than the oilto be clesulfurlzed and preferably less than about 0.15% sulfur.

Naphtha fractions of the type described are readily available,inexpensive and quite satisfactory. They may be improved somewhat forthe present purpose, however, by the addition of a small amount (forinstance, 0.5 to 10%) of a phenolic compound such as phenol, cresol,o=cyclohexylphenol or 1,2,3, i-tetrahydro--hydroxynaphthalene.

In order that the desulfurization may be effected under the describedconditions it is necessary that the reaction mixture be maintained at ahigh density. This condition is obtained firstly by working in theabsence of added hydrogen or other gases, secondly by choosing a lowerboiling hydrocarbon oil which is not too volatile, thirdly, by choosingconditions of temperature and space velocity affording a minimum amountof cracking and dehydrogenation, and fourthly, by imposing a very highpressure. Thus, it is necessary that the pressure be sufiicient tomaintain the hydrocarbon mixture in the reaction zone at a density of atleast 0.25 g./cc. and preferably at least 0.30 g./oc. The material undera pressure above the critical pressure and at a temperature above thecritical temperature is sometimes referred to as being in asupercritical dense phase. The specified density is necessary in orderto prevent precipitation of tarry deposits on the catalyst.Theoretically, there is no upper limit to the pressures that may beapplied; however, a practical upper limit in the order of 1000atmospheres'is set by the available apparatus.

The process of the invention will be further illustrated by thefollowing specific example.

Example The process of the invention was applied in the desulfurizationof a gas oil having the fol lowing inspection data:

Gas Oil Naphtha Density, 20/4 Bromine Numbc Aniline Point, C CriticalTemperature, calc Sulfur, per cent by wt ASliM Distillation:

A quantity (1.15 volumes) of a lower boiling naphtha fraction having theinspection data indicated the-above table was added to produce a blendhaving a critical temperature of about 368 C. The naphtha contained byweight 5.2% aromatics, 53.4% naphthenes and 41.4% parafflns. The mixturewas passed at a space velocity of 1 (based on the gas oil) in theabsence of hydrogen or other gas through a bed of catalyst whilemaintaining a temperature of 400 C. and a pressure kg./cm. sufhcient tocompress the reaction mixture to a density of 0.35 g./cc. The naphthafraction was recovered substantially unchanged from the desulfurized gasoil. As seen in the above data the untreated gas oil contained 0.65%sulfur. The treated gas oil contained 0.08% sulfur during the firsthours of opera-- tion, after which the sulfur content increased to 0.19%at the end of 300 hours.

The catalyst in this particular case was prepared by treating anactivated alumina with hydrochloric acid, impregnating it with cobaltnitrate and ammonium molybdate, and calcining in a current of nitrogenat 370 C. It contained 7 parts of cobalt plus molybdenum, in an atomicratio of 1 to 5, per 93 parts of alumina.

In other experiments with the same'gas oil and catalyst and undersubstantially the same conditions, but without the added naphtha, andhence in the liquid phase, the desulfurization activity. of theycatalyst declined at a rapid rate. At the end of 100 hours. of operationthe treated gas oil already contained about 0.3% sulfur.

In still another case where a parafiinic oil, e. g. octane, was.substituted for the naphtha. the sulfur content of the treated gas oilrose rapidly to over 0.5% sulfur in less than 100 hours.

Also. when operating in the vapor phase the activity of the catalyst. isquickly poisoned unless alarge amount of hydrogen is added. Even whenoperating in the vapor phase in the presence of large amount ofhydrogen, it is not possible to supply the required hydrogen by thesimultaneous dehydrogenation of added naphthenic hydrocarbons. Forexample, in the vapor phase desulfurization of No. 1 range fuel (Ex WestTexas. petroleum) boiling between about 182 C. and, 252 C. in the.presence of recycled hydrogen a methylcyclohexane concentrate was addedin amounts up to 40 7G. The process was dependent in all cases upon anexternal source of hydrogen. All attempts to supply the hydrogen by thedehydrogenation of the added methylcyclohexane were unsuccessful due tothe inception of substantial cracking (which consumes large amounts ofhydrogen) as soon as the temperature was increased sufiiciently toestablish dehydrogena ing conditions.

As pointed out, the desulfurization when operating according to thepresent invention is not efiected through the use of added hydrogen andadded gas is detrimental. The small amount of hydrogen required for thedesulfurization reaction is supplied by hydrogen exchange within the oilitself. No appreciable amount of dehydrogenation of hydrocarbonconstituents in the oil to give free hydrogen takes place at thetemperatures used. The process, therefore, is not one which is carriedout in the conventional way with hydrogen while attempting to supply therequired hydrogen by the simultaneously dehydrogenating added naphthenichydrocarbons. When a naphthenic naphtha, such as that illustrated, isused to depress the critical temperature, the naphtha, therefore,suffers little change. It is, therefore. desirable in some cases torecycle the naphtha to the reaction zone after separating it from thedesulfurized oil. Before reusing the naphtha it is desirable to free itsubstantially of dissolved hydrogen sulfide.

We claim as our invention:

1. The method of desulfurizing ahydrocarbon oil having a mid-boilingpoint (ASTM) "of at least 250 C. and having at least 0.5% of organicallycombined sulfur which comprises adding to said oil to be desulfurized arecycled naphtha of lower sulfur content boiling substantially withinthe range of 106 C. and 205 C. and containing not more than 50% paraffmsin an amount sufiicient to, reduce the critical temperature or themixture to at least 20 C. below the desired working to: perature, thencontracting the resulting mixture in the absence of added gas and in theabsence of a liquid phase as. a homogeneous supercritical dense phasewith a molybdenum oxide-cobalt oxide-aluminum oxide catalyst containingmolybdenurn and cobalt in an atomic ratio of about 1:5 at a temperatureabove the critical tempera-- ture of the mixture and between 375 C. and.425 C. while compressed to a density of at least 0.30 g./cc., separatingthe said naphtha from the desulfurizcd oil, and recycling the saidseparated naphtha for the treatment of further quantities of said oil tobc desulfurized.

2. The method for desulfurizlng a hydrocar- 8 bon oil having amid-boiling point ASTM). of at least 200 C. and having organically boundS111!- fur impurities which comprises adding to the said oil to bedesulfurized a lower boiling naphthenic hydrocarbon distillate in anamount sufficient to reduce the critical temperature of the resultingmixture to at least 20 C. below the desired operating temperature, thencontacting-the resulting mixture as a homogeneous supercritical densephase in the absence of added gas with a sulfactive hydrogenationcatalyst at a temperature at least 20 C. above the critical temperatureof the mixture and between 325 C. and 450 C. while compressed to adensity of at least 0.25 g./cc., separating the said lower boilinghydrocarbon distillate from the desulfurized hydrocarbon oil, and addingsaid separated lower boiling hydrocarbon distillate to a fresh quantityof. the said oil to be desulfurized as above specified.

3. The method for desulfurizing a hydr0car bon oil having a mid-b0llingpoint (AS'I'M) of at least 250 C. and having organically bound sulfurimpurities which comprises adding to the oil to be desulfurized a lowerboiling non-paraffinic hydrocarbon oil in an amount. sulficientto reducethe critical temperature of the resulting mixture to at least 20 0.below the operating temperature, then contracting the resulting mixturein the absence of added hydrogen and in the absence of a liquid phasewith a molybdenum oxide-cobalt oxide-aluminium oxide catalyst at. a.temperature at least 20 C. above the. critical temperature of themixture and between 325 C. and 450 C. while compressed to a density ofat least 0.25 g./cc., and then separating the said lower boilinghydrocarbon oil from the desulfurized hydrocarbon oil.

The method for desulfurizing a hydrocarbon oil boiling above thegasoline boiling range or. having organically bound sulfur impuritieswhich comprises adding to'the oil to be desulfurized a lower boilingstraight run fraction of naphthenic petroleum in an amount suiiicient toreduce the critical temperature of the resulting mixture to at least 20C. below the operating per-ature, then contacting the resulting mixturein the absence of added gas with a sulfactive hydrogenation catalyst ata temperature at least 20 C. above the critical emperature of themixture and, between 3'75 C. and 425 C. while comto a density oi atleast.0.25 g./cc., and then separating the said lower boiling fractionfrom the desuliurized hydrocarbon oil.

5. The method for desulfurizing a hydrocarbon oil having a mid-boilingpoint (ASTM) of at least 200 C. and having at least 0.5% of organicallybound sulfur which comprises adding tothe. hydrocarbon oil to bedesulfurizeol a lower boiling naphtha containing not more than 50%paraffins in an amount sufficient to reduce the critical temperature ofthe mixture to at least 23 C. below the desired operating temperature.then contacting the resulting mixture in the absence of added gas with asulfactive hydrogenation catalyst at a temperature at least 20 0. abovethe critical temperature of the mixture and between 325 C. and 450C.while compressed to a density of at least 0.3 g./cc., and thenseparating the said naphtha from the desulfurized hydrocarbon oil.

5. The method for desuliurizing a sulfur-bearing hydrocarbon oil boilingabove the gasoline boiling range which comprises adding to thehydrocarbon oil to be desulfurized a lower boiling naptha. of lessersulfur content and. containing not more than 50% paraflins in an amountsufflcient to reduce the critical temperature of the mixture to at least20 0. below the desired operating temperature, then contacting theresulting mixture in the absence of added hydrogen with a sulfactivehydrogenation catalyst at a temperature at least 20 0. above thecritical temperature of the mixture and between 325 C. and 450 C. whilecompressed to a density of at least 0.25 g./cc., and then recovering thesaid naphtha from the desulfurized hydrocarbon oil.

WILLEM FREDERIK ENGEL. PETER VAN r SPIJKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

Number 10 UNITED STATES PATENTS Name Date Rosen Aug. 19, 1941 SchulzeFeb. 17, 1942 Bent et al Feb. 8, 1944 Hays June 12, 1945 Huffman Mar. 9,1948 Byrns July 20, 1948

4. THE METHOD FOR DESUFLURIZING A HYDROCARBON OIL BOILING ABOVE THEGASOLINE BOILING RANGE AND HAVING ORGANICALLY BOUND SULFUR IMPURITIESWHICH COMPRISES ADDING TO THE OIL TO BE DESULFURIZED A LOWER BOILINGSTRAIGHT RUN FRACTION OF A NAPHTHENIC PETROLEUM IN AN AMOUNT SUFFICIENTTO REDUCE THE CRITICAL TEMPERATURE OF THE RESULTING MIXTURE TO AT LEAST20* C. BELOW THE OPERATING TEMPERATURE, THEN CONTACTING THE RESULTINGMIXTURE IN THE ABSENCE OF ADDED GAS WITH A SULFACTIVE HYDROGENATIONCATALYST AT A TEMPERATURE AT LEAST 20* C. ABOVE THE CRITICAL TEMPERATUREOF THE MIXTURE AND BETWEEN 375* C. AND 425* C. WHILE COMPRESSED TO ADENSITY OF AT LEAST 0.25 G./CC., AND THEN SEPARATING THE SAID LOWERBOILING FRACTION FROM THE DESULFURIZED HYDROCARBON OIL.